1. Field of the Invention
The present invention relates to a bubbler for vaporizing a precursor for thin film deposition.
2. Description of the Related Art
In metal-organic chemical vapor deposition (MOCVD) processes, a precursor (source) for thin film deposition is vaporized in a bubbler and then carried along with carrier gas into a reaction chamber. Here, the amount of precursor supplied into the reaction chamber is influenced by parameters including the bubbler""s temperature and pressure and the flow rate of the carrier gas. Thus, such parameters that determine the amount of precursor exhausted from the bubbler must be accurately controlled to deposit a thin film to a desired thickness.
FIG. 1 is a sectional view of a conventional bubbler for use in vaporizing a liquid source. The bubbler shown in FIG. 1 has a carrier-gas inlet tube 12, which is immersed in the liquid source 14 in a container 11, and an exhaust tube 13 set above the surface of the liquid source 14. A carrier gas 15 supplied through the carrier-gas inlet tube 12 forms bubbles, and the liquid source 14 is carried by a stream of carrier-gas bubbles through the exhaust tube 13. The carrier gas 15 in the form of bubbles increases the contact area with the liquid source 14, and thus this vaporization technique has the advantage of high source supply efficiency. However, the vaporization efficiency of the above bubbler is low when a less vaporizable source is used. Thus, the sources which can be used in the bubbler are limited.
To account for this problem, another bubbler as shown in FIG. 2 was suggested. The conventional bubbler of FIG. 2 includes a porous plate 28, which is positioned at the middle of a vaporizer chamber 21 to enhance the vaporization efficiency of a less vaporizable source, and a heater 27, which is installed close to the outer wall of the vaporizer chamber 21 to heat the vaporizer chamber 21. In the bubbler, a liquid source supplied through a source inlet tube 22 is vaporized while passing through the porous plate 28 heated by the heater 27, and exhausted through an exhaust tube 26, along with a carrier gas supplied through a carrier-gas inlet tube 23. The vaporization efficiency thus can be improved. However, there are problems in that the temperature distribution in the vaporizer chamber 21 varies according to the proximity to the heater 27, and the vaporization efficiency of the source is nonuniform over the porous plate 28.
Another drawback of the bubbler shown in FIG.1 is found when a solid source is applied to the bubbler. Referring to FIG. 3, as a carrier gas 35 is supplied through the carrier-gas inlet tube 12 into a solid source 34 in the container 11, the carrier gas 35 forms a gas tunnel 36 while carrying the solid source 34. Here, the width and depth of the gas tunnel 36 are enlarged over time with use of the bubbler. Also, as the size of the gas tunnel 36 increases, the amount of solid source 34 carried by the carrier gas 35 varies, so that the amount of source supplied into a reaction chamber (not shown) cannot be accurately controlled. In addition, if the gas tunnel 36 is enlarged too much to carry the solid source 34, the bubbler must be replaced by new one although a considerable amount of solid source 34 yet remains in the container 11. Thus, there is a problem of waste of source.
Another example of a bubbler for solid sources is shown in FIG. 4. The conventional bubbler of FIG. 4 has a compressing plate 47 seated on a solid source 44 contained in a vaporizer chamber 41, and a porous plate 48 on which the solid source 44 is put. An exhaust tube 43 is connected to the top of the vaporizer chamber 41, separated a predetermined distance from the compressing plate 47, and a porous filter 49 is fitted to the exhaust tube 43 so as to prevent leakage of the unvaporized solid source. A carrier-gas inlet tube 42 is connected to the vaporizer chamber 41 near the bottom thereof. In the bubbler, a carrier gas supplied through the carrier-gas inlet tube 42 enters the solid source 44 through the porous plate 48, which allows uniform and wide contact between the solid source 44 and the carrier gas. However, the bubbler also fails to effectively vaporize less vaporizable sources, such as Sr(thd)2 and Ba(thd)2. Thus, the applicable sources are limited.
It is a feature of the present invention to provide a bubbler capable of controlling the amount of source being vaporized therein with improved vaporization efficiency, and thus to loosen the limitation of applicable sources.
In accordance with one aspect of the present invention, there is provided a bubbler including a vaporizer chamber, the vaporizer chamber having defined therein a source inlet hole, an exhaust hole and a carrier gas inlet hole; a source supply unit connected to the source inlet hole; a plate installed in the vaporizer chamber, the plate being adapted to receive a source entering into the vaporizer chamber; and a heater source installed in the vaporizer chamber, the heater source being adapted to evenly heat the plate.
Preferably, the heater source has an area that is larger than the area of the facing porous plate, and the plate is a porous plate having pores capable of capturing the source. Preferably, the bubbler further comprises source diffusing means disposed in the vaporizer chamber, for causing the source to uniformly diffuse into the plate.
Other features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.